Solid-state imaging device and radiation imaging system

ABSTRACT

N + -type semiconductor regions  12   d  are formed on a front surface side of a p − -type layer  12   c  of a semiconductor substrate  12 , and these n + -type semiconductor and p − -type semiconductor constitute photodiodes. A metal wire  14  connected to an isolation region  12   e  is formed on a first insulating layer  13 . The metal wire  14  is provided so as to extend along a row direction and along a column direction between adjacent n + -type semiconductor regions  12   d , and is of grid shape when viewed from a direction of incidence of light. Signal readout lines  53  are formed on a third insulating layer  16 . The signal readout lines  53  are made of metal such as aluminum, are located above the n + -type semiconductor regions  12   d  when viewed from the direction of incidence of light, and are provided so as to extend along the column direction.

TECHNICAL FIELD

The present invention relates to a solid-state imaging apparatus and aradiographic imaging apparatus.

BACKGROUND ART

An example of the known solid-state imaging apparatus of this type isone having a plurality of photoelectric converters arrayed in a matrixof M rows and N columns on a substrate, and signal readout lines (signallines) for readout of signals from the respective photoelectricconverters (e.g., reference is made to Patent Document 1). The signalreadout lines are provided so as to extend along the direction ofcolumns and between adjacent photoelectric converters.

[Patent Document 1] PCT International Publication WO00/26966

DISCLOSURE OF THE INVENTION

In the configuration of the conventional technology, however, eachsignal readout line (signal line) comes to have a capacitance (parasiticcapacitance) with respect to an electrically conductive material locatedbetween adjacent photoelectric converters (e.g., a gate line connectinga control terminal of each gate switch connected to the signal line, toa vertical shift register; a metal wire for giving a predeterminedpotential (including the ground potential) to an isolation region formedbetween adjacent photoelectric converters). The parasitic capacitanceposes a problem of noise generation. Particularly, in a case where animage detecting area has a large area, the length of the signal lineitself becomes long, so as to increase the parasitic capacitance aswell, so that noise becomes more likely to be generated.

The present invention has been accomplished in view of the above pointand an object of the invention is to provide a solid-state imagingapparatus and a radiographic imaging apparatus capable of reducing theparasitic capacitance of signal lines for readout of signal outputs fromphotoelectric converters and thereby suppressing generation of noise.

A solid-state imaging apparatus according to the present inventioncomprises: a plurality of photoelectric converters arrayed in atwo-dimensional pattern; and signal lines for reading out outputs fromthe photoelectric converters, which are electrically connected to thephotoelectric converters, wherein the signal lines are located above thephotoelectric converters.

In the solid-state imaging apparatus according to the present invention,the signal lines for readout of outputs from the photoelectricconverters are located above the photoelectric converters, and thus areapart from portions between adjacent photoelectric converters. For thisreason, the parasitic capacitance of the signal lines is reduced, sothat the generation of noise can be suppressed.

Preferably, the signal lines are provided for respective columns of thephotoelectric converters and extend along a direction of each column;the solid-state imaging apparatus further comprises a switch groupconsisting of a plurality of switches for controlling electricalconnection and disconnection between each photoelectric converter andthe signal line in each column of the photoelectric converters, andwires connected to control terminals of the respective switchesconstituting the switch group and arranged to supply to the controlterminals a scan signal to turn each switch off or on in each row of thephotoelectric converters; the wires are provided so as to extend along adirection of rows of the photoelectric converters and between thephotoelectric converters adjacent to each other.

Another solid-state imaging apparatus according to the present inventioncomprises: a plurality of photoelectric converters arrayed in a matrixof M rows and N columns; first wires provided for the respectivecolumns; a first switch group consisting of a plurality of switchesconnecting between each photoelectric converter and the first wire ineach column; a vertical shift register for outputting a vertical scansignal to open and close each switch forming the first switch group, ineach row; second wires for connecting between a control terminal of eachswitch forming the first switch group, and the vertical shift registerin each row; a second switch group consisting of a plurality of switchesconnecting between each first wire and a signal output line; and ahorizontal shift register for outputting a horizontal scan signal toopen and close each switch forming the second switch group, in eachcolumn, wherein the first wires are located above the photoelectricconverters and provided so as to extend along a direction of thecolumns, and wherein the second wires are provided so as to extend alonga direction of the rows and between the photoelectric convertersadjacent to each other.

In the solid-state imaging apparatus according to the present invention,the signal lines for readout of signal outputs from the photoelectricconverters are located above the photoelectric converters, and thus areapart from portions between adjacent photoelectric converters. For thisreason, the parasitic capacitance of the signal lines is reduced, sothat the generation of noise can be suppressed.

A radiographic imaging apparatus according to the present inventioncomprises the foregoing solid-state imaging apparatus; and ascintillator for converting radiation to visible light, which isprovided so as to cover the plurality of photoelectric converters.

In the radiographic imaging apparatus according to the presentinvention, as described above, the parasitic capacitance of the signallines in the solid-state imaging apparatus is reduced, so that thegeneration of noise can be suppressed in similar fashion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view for explaining a cross-sectionalconfiguration of a radiographic imaging apparatus according to anembodiment of the present invention.

FIG. 2 is a schematic view for explaining the cross-sectionalconfiguration of the radiographic imaging apparatus according to theembodiment of the present invention.

FIG. 3 is a plan view showing the radiographic imaging apparatusaccording to the embodiment of the present invention.

FIG. 4 is a configuration diagram showing the radiographic imagingapparatus according to the embodiment of the present invention.

FIG. 5 is a plan view showing a photosensitive section included in asolid-state image sensor of the radiographic imaging apparatus accordingto the embodiment of the present invention.

FIG. 6 is a schematic view for explaining a cross-sectionalconfiguration along line VI-VI in FIG. 5.

FIG. 7 is a schematic view for explaining a cross-sectionalconfiguration along line VII-VII in FIG. 5.

FIG. 8 is a schematic view for explaining a cross-sectionalconfiguration along line VIII-VIII in FIG. 5.

FIG. 9 is a schematic view for explaining a cross-sectionalconfiguration along line IX-IX in FIG. 5.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will be described belowin detail with reference to the drawings. Identical elements or elementswith identical functionality will be denoted by the same referencesymbols in the description, without redundant description. Aradiographic imaging apparatus according to the present embodimentincorporates a solid-state imaging apparatus (solid-state image sensor)according to an embodiment of the present invention.

FIGS. 1 and 2 are schematic views for explaining a cross-sectionalconfiguration of the radiographic imaging apparatus according to thepresent embodiment, and FIG. 3 is a plan view showing the radiographicimaging apparatus according to the present embodiment. FIG. 4 is aconfiguration diagram showing the radiographic imaging apparatusaccording to the present embodiment. FIG. 3 is depicted withoutillustration of bonding wires.

The radiographic imaging apparatus 1 of the present embodiment, as shownin FIGS. 1 to 3, has a solid-state image sensor 11, a scintillator 21, amount substrate 23, a frame 25, and others.

The solid-state image sensor 11 is an MOS image sensor, and has aphotosensitive section 31, a shift register section 41, and anamplification section 51, which are formed on one side of asemiconductor substrate 12. In this manner, the photosensitive section31, the shift register section 41, and the amplification section 51 areformed on the same substrate (semiconductor substrate 12). Thesemiconductor substrate 12 (solid-state image sensor 11) is fixed on themount substrate 23. In the present embodiment, the area of thesemiconductor substrate 12 is approximately 16900 mm² (=130 mm×130 mm),and the area of the photosensitive section 31 approximately 15625 mm²(=125 mm×125 mm).

The photosensitive section 31, as shown in FIG. 4, is constructed in aconfiguration wherein a plurality of photodiodes (photoelectricconverters) 33 for storing charges according to intensities of incidentlight are arrayed in a two-dimensional pattern on the semiconductorsubstrate 12. More specifically, the photosensitive section 31 iscomposed of M×N photodiodes 33 arrayed in a matrix of M rows in they-axis direction and N columns in the x-axis direction (M and N arenatural numbers). In FIG. 4, M and N are determined to be “4.”

Each of the photodiodes 33 forming the photosensitive section 31 isprovided with a gate switch (switch forming a first switch group) 35 oneend of which is electrically connected to the photodiode 33 and theother end of which is electrically connected to a signal readout linedescribed later. Therefore, during an opening period of the gate switch35, a charge is stored in the photodiode 33 with incidence of light, andthe charge stored in the photodiode 33 is read out to thelater-described signal readout line with closure of the gate switch 35.The gate switch 35 can be constructed of an MOSFET (field effecttransistor).

The shift register section 41 includes a vertical shift register 43 andis formed so as to face one side of the photosensitive section 31, onthe semiconductor substrate 12. The vertical shift register 43 outputs avertical scan signal to open and close each gate switch 35.

A control terminal of each gate switch 35 is electrically connected tothe vertical shift register 43 by a gate line (second wire) 45. In thisconfiguration, each gate switch 35 can be opened and closed by avertical scan signal outputted from the vertical shift register 43.Specifically, the gate lines 45 extend in the x-axis direction throughportions between rows of photodiodes 33 arrayed in the photosensitivesection 31, and each gate line 45 is connected to the control terminalsof the respective gate switches 35 existing in one row. Accordingly, thevertical shift register 43 and the control terminals of the gateswitches 35 are connected on a row-by-row basis.

Furthermore, N signal readout lines (first wires; signal lines) 53, towhich the other ends of the gate switches 35 are electrically connectedin each column, are provided between columns of photodiodes 33 arrayedin the photosensitive section 31. The N signal readout lines 53 areelectrically connected to the amplification section 51. Theamplification section 51 includes charge amplifiers 55, readout switches(switches constituting a second switch group) 57, a horizontal shiftregister 59, and so on. The amplification section 51 is formed so as toface one side adjacent to the one side of the photosensitive section 31which the shift register section 41 is formed so as to face, on thesemiconductor substrate 12.

The charge amplifiers 55 are provided for the respective signal readoutlines 53, and amplify charges (electric current outputs), which is readout into the signal readout lines 53. The readout switches 57 areprovided for the respective signal readout lines 53 and output thecharges (electric current outputs), which is read out of the photodiodes33, to a signal output line 60. The horizontal shift register 59 outputsa horizontal scan signal to open and close each readout switch 57.

A plurality of bonding pads 61 electrically connected to the amplifiersection 51 are formed on the semiconductor substrate 12, as shown inFIGS. 2 and 3. These bonding pads 61 are electrically connected tocorresponding bonding pads 65 formed on the mount substrate 23, bybonding wires 63. In this configuration, the outputs from theamplification section 51 are supplied via the mount substrate 23 to theoutside of the imaging apparatus 1. A plurality of bonding pads 67electrically connected to the shift register section 41 are formed onthe semiconductor substrate 12 (particularly, cf. FIG. 3). These bondingpads 67 are electrically connected to corresponding bonding pads 69formed on the mount substrate 23, by bonding wires (not shown). In thisconfiguration, signals from the outside of the imaging apparatus 1 aresupplied via the mount substrate 23 to the shift register section 41.

The scintillator 21 converts incident radiation (e.g., X-rays) tovisible light and is of columnar structure. The scintillator 21, as alsoshown in FIG. 3, is arranged to cover the region where thephotosensitive section 31, the shift register section 41, and theamplification section 51 are formed on one side of the semiconductorsubstrate 12, and is formed directly on the region. In thisconfiguration, the scintillator 21 is arranged in contact with theregion where the photosensitive section 31, the shift register section41, and the amplification section 51 are formed on one side of thesemiconductor substrate 12. The region where the bonding pads 61, 67 areformed on one side of the semiconductor substrate 12 is not covered bythe scintillator 21, and is exposed.

A variety of materials can be used for the scintillator 21, and one ofpreferred materials is T1 (thallium) doped CsI, which demonstrates goodluminous efficiency. A protective film (not shown) for hermeticallysealing the scintillator 21 while covering the columnar structure of thescintillator 21 so as to fill its gaps is formed on the scintillator 21.The protective film is preferably a material that transmits radiationbut shields against water vapor, e.g., poly-para-xylylene (trade nameParylene, available from Three Bond Co., Ltd.), and particularlypreferably, poly-para-chloroxylylene (trade name Parylene C, availablefrom the same company). In the present embodiment, the thickness of thescintillator 21 is approximately 300 μm.

The scintillator 21 can be formed by growing columnar crystals of CsI bydeposition method. The protective film can be formed by CVD. The methodsof forming the scintillator 21 and the protective film are disclosed indetail in PCT International Publication WO98/36290 filed by Applicant ofthe present application, for example, and the description thereof isomitted herein.

The frame 25 is fixed on the mount substrate 23 so as to surround thesolid-state image sensor 11. The frame 25 has an opening 27 ofrectangular shape formed at the position corresponding to thephotosensitive section 31, and radiation is incident through the opening27 to the scintillator 21. A space S is created between the frame 25,and the semiconductor substrate 12 and the mount substrate 23. The shiftregister section 41 and the amplification section 51 of the solid-stateimage sensor 11, the bonding pads 61, 65, the bonding wires 63, etc. arelocated inside the space S. Since the bonding wires 63 are placed insidethe space S defined by the frame 25, the semiconductor substrate 12, andthe mount substrate 23 as described above, the bonding wires 63 areprotected from external physical stress, without being pushed by theframe 25. In addition, a shield 29 of a radiation-shielding material(e.g., lead or the like) is provided on the side opposite to theamplification section 51 side, on the frame 25, and the shield 29 wellshields against radiation. In the present embodiment, the thickness ofthe shield 29 is approximately 2.5 mm.

Next, the configuration of the photosensitive section 31 will bedescribed on the basis of FIGS. 5 to 9. FIG. 5 is a plan view showingthe photosensitive section. FIG. 6 is a schematic view for explaining across-sectional configuration along line VI-VI in FIG. 5. FIG. 7 is aschematic view for explaining a cross-sectional configuration along lineVII-VII in FIG. 5. FIG. 8 is a schematic view for explaining across-sectional configuration along line VIII-VIII in FIG. 5. FIG. 9 isa schematic view for explaining a cross-sectional configuration alongline IX-IX in FIG. 5. FIG. 5 is depicted without illustration of firstto fourth insulating layers 13, 15-17, and the gate switches 35.

The semiconductor substrate 12, as shown in FIGS. 6 to 9, includes ap⁺-type semiconductor substrate 12 a, and a p⁻-type epitaxialsemiconductor layer 12 b and a p⁻-type layer 12 c are formed on thep⁺-type semiconductor substrate 12 a. The p⁺-type semiconductorsubstrate 12 a is set at the ground potential. The solid-state imagesensor 11 is one using Si as a semiconductor; “high concentration”refers to the impurity concentration of not less than about 1×10¹⁷/cm³and is expressed by “+” attached to the conductivity type; “lowconcentration” refers to the impurity concentration of not more thanabout 1×10¹⁵/cm³ and is expressed by “−” attached to the conductivitytype.

N⁺-type semiconductor regions 12 d are formed on the front surface sideof the p⁻-type layer 12 c, and a pn junction composed of each n⁺-typesemiconductor (n⁺-type semiconductor region 12 d) and the p⁻-typesemiconductor (p⁻-type layer 12 c) constitutes a photodiode(photoelectric converter) 33. The n⁺-type semiconductor regions 12 deach are of rectangular shape when viewed from the direction ofincidence of light, and are arrayed in a two-dimensional pattern of Mrows and N columns, as shown in FIG. 5. In this configuration, thephotodiodes 33 are arrayed in the two-dimensional pattern of M rows andN columns in the photosensitive section 31. In the present embodiment,the length on each side of the n⁺-type semiconductor regions 12 d is setto be approximately 50 μm.

An isolation region 12 e of a p⁺-type semiconductor is formed betweenadjacent n⁺-type semiconductor regions 12 d on the front surface side ofthe p⁻-type layer 12 c. The isolation region 12 e, as shown in FIG. 5,extends along the row direction and along the column direction betweenadjacent n⁺-type semiconductor regions 12 d and is of grid shape whenviewed from the direction of incidence of light.

A first insulating layer (e.g., made of a silicon oxide film) 13 isformed on the p⁻-type layer 12 c, the n⁺-type semiconductor regions 12d, and the isolation region 12 e. A metal (e.g., aluminum) wire 14 iselectrically connected to the isolation region 12 e via through holesformed in the first insulating layer 13. The metal wire 14, as shown inFIG. 5, is provided so as to extend along the row direction and alongthe column direction between adjacent n⁺-type semiconductor regions 12d, and is of grid shape when viewed from the direction of incidence oflight. In the present embodiment, the width of the metal wire 14 is setgreater than the distance between adjacent n⁺-type semiconductor regions12 d, and part of the metal wire 14 overlaps the edges of n⁺-typesemiconductor regions 12 d when viewed from the direction of incidenceof light. The metal wire 14 is grounded and thus the isolation region 12e is set at the ground potential. The metal wire 14 may also beconnected to a fixed potential, instead of being grounded.

A second insulating layer (e.g., made of a silicon oxide film) 15 isformed on the first insulating layer 13. The aforementioned gate lines45 and a third insulating layer (e.g., made of a silicon oxide film) 16are formed on the second insulating layer 15. The gate lines 45 are madeof metal such as aluminum, and are provided so as to extend along therow direction and between adjacent n⁺-type semiconductor regions 12 d.

The aforementioned signal readout lines 53 and a fourth insulating layer(e.g., made of a silicon oxide film) 17 are formed on the thirdinsulating layer 16. The signal readout lines 53 are made of metal suchas aluminum, and, as shown in FIGS. 5 and 6, the signal readout lines 53are located above the n⁺-type semiconductor regions 12 d when viewedfrom the direction of incidence of light, and are provided so as toextend along the column direction. In the present embodiment, the widthof the signal readout lines 53 is set to be approximately 0.5 μm. Thesignal readout lines 53 are placed with deviation of approximately 1-20μm from one side of n⁺-type semiconductor regions 12 d, above then⁺-type semiconductor regions 12 d.

In the present embodiment, as described above, the signal readout lines53 are located above the n⁺-type semiconductor regions 12 d constitutingthe photodiodes 33, and are thus separated from the portions betweenadjacent n⁺-type semiconductor regions 12 d, i.e., from the metal wire14. This reduces the parasitic capacitance of the signal readout lines53 and thus suppresses generation of noise, thereby improving the SNratio.

Since the signal readout lines 53 are located above the n⁺-typesemiconductor regions 12 d, the photosensitivity of the photodiodes 33becomes lower (by about 1.6% in the present embodiment) than that in aconfiguration wherein the signal readout lines 53 are located betweenadjacent n⁺-type semiconductor regions 12 d. However, this decrease ofthe photosensitivity can be compensated for by a technique of enhancingthe amplification rate in the amplification section 51, or the like,whereby a decrease of image output can be prevented as a result.

In order to reduce the parasitic capacitance of the signal readout lines53, it is preferable to increase the deviation amount from one side ofn⁺-type semiconductor regions 12 d (the portions between adjacentn⁺-type semiconductor regions 12 d), e.g., to place the signal readoutlines 53 in the central portion of the n⁺-type semiconductor regions 12d when viewed from the direction of incidence of light. However, suchlarge deviation from one side of n⁺-type semiconductor regions 12 d isnot practical, because the signal readout lines 53 need to be connectedto the gate switches 35 (MOSFETs). For this reason, the aforementioneddeviation amount is preferably set in consideration of the decreaseamount of the parasitic capacitance and connectivity to the gateswitches 35.

The present invention is by no means limited to the above embodiment.The scintillator 21 is formed directly on the semiconductor substrate 12in the present embodiment, but the structure is not limited to this. Forexample, it is also possible to adopt a configuration wherein ascintillator substrate is formed by laying a scintillator on aradiation-transmitting substrate and wherein the scintillator substrateis arranged so as to keep the scintillator in contact with the regionwhere the photosensitive section 31, the shift register section 41, andthe amplification section 51 are formed on one side of the semiconductorsubstrate 12. In a case where a protective film is formed on thescintillator, the protective film is brought into contact with theregion where the photosensitive section 31, the shift register section41, and the amplification section 51 are formed.

INDUSTRIAL APPLICABILITY

The solid-state imaging apparatus and the radiographic imaging apparatusof the present invention are applicable to radiographic imaging systemsof large area, particularly, used in medical and industrial X-rayphotography.

1. A solid-state imaging apparatus comprising: a plurality ofphotoelectric converters arrayed in a two-dimensional pattern; signallines for reading out outputs from the photoelectric converters, whichare electrically connected to the photoelectric converters, wherein thesignal lines are located above the photoelectric converters.
 2. Thesolid-state imaging apparatus according to claim 1, wherein the signallines are provided for respective columns of the photoelectricconverters and extend along a direction of each column, the solid-stateimaging apparatus further comprising: a switch group consisting of aplurality of switches for controlling electrical connection anddisconnection between each photoelectric converter and the signal linein each column of the photoelectric converters; and wires connected tocontrol terminals of the respective switches constituting the switchgroup and arranged to supply to the control terminals a scan signal toturn each switch off or on in each row of the photoelectric converters,wherein the wires are provided so as to extend along a direction of rowsof the photoelectric converters and between the photoelectric convertersadjacent to each other.
 3. A solid-state imaging apparatus comprising: aplurality of photoelectric converters arrayed in a matrix of M rows andN columns; first wires provided for the respective columns; a firstswitch group consisting of a plurality of switches connecting betweeneach photoelectric converter and the first wire in each column; avertical shift register for outputting a vertical scan signal to openand close each switch forming the first switch group, in each row;second wires for connecting between a control terminal of each switchforming the first switch group, and the vertical shift register in eachrow; a second switch group consisting of a plurality of switchesconnecting between each first wire and a signal output line; and ahorizontal shift register for outputting a horizontal scan signal toopen and close each switch forming the second switch group, in eachcolumn, wherein the first wires are located above the photoelectricconverters and provided so as to extend along a direction of thecolumns, and wherein the second wires are provided so as to extend alonga direction of the rows and between the photoelectric convertersadjacent to each other.
 4. A radiographic imaging apparatus comprising:the solid-state imaging apparatus as set forth in any one of claims 1 to3; and a scintillator for converting radiation to visible light, whichis provided so as to cover the plurality of photoelectric converters.